1. Field of the Invention
This invention relates to an optoelectronic integrated circuit including an optical bistable circuit.
2. Description of the Prior Art
An optical gate device which is capable of controlling loss or gain of light transmitted therethrough in accordance with a current injected thereto is known as a loss modulator or laser amplifier using a semiconductor laser. For example, C.H. Henry et al. in Journal of Applied Physics, vol. 51, page 3042, 1980, describes such a device as follows:
A loss or gain of a transmitted light ray whose wavelength is around lasing wavelength, in an active layer of a semiconductor laser, varies with a magnitude of a current injected thereto. When a current is not injected, the transmitted light ray is subjected to 100-200 cm.sup.-1 loss. The loss decreases with increase in the magnitude of the injected current. Further injection of the current provides a gain of light. It is the loss modulator to modulate the transmitted light ray in intensity by injection of the current. On the other hand, it is the laser amplifier to amplify the transmitted light ray with a gain.
Generally, an active waveguide of a semiconductor laser is formed in parallel to the plane of its substrate. The loss modulator and laser amplifier also guide a transmitted light ray in the direction papallel to the plane of the substrate generally. However, when such a loss modulator and laser amplifier are applied to a system utilizing parallelism of light beams, which system is capable of large scale parallel processing, it is desired that the light beam be inputted or emitted perpendicularly with respect to the plane of the substrate to improve integration scale of devices and make construction of the system easier. As a semiconductor laser emitting a laser beam perpendicularly with respect to the plane of the substrate, for example, H. Soda et al. described a surface emitting laser at IEEE Journal of Quantum Electronics, vol. QE-19, page, 1035, 1983, which is shown in FIG. 8. The surface emitting laser comprises an InGaAsP active layer 1 sandwiched between p-InP first clad layer 2 and n-InP second clad layer 3' similar to the conventional semiconductor laser. This laser further comprises first and second reflection mirrors 4 and 5 so that a laser beam 6 is emitted perpendicularly with respect to the plane of the substrate.